1. Field of the Invention
The present invention relates to an exposure apparatus which illuminates an original by an illumination optical system, and projects the pattern of the original onto a substrate, a method of controlling the same, and a method of manufacturing a device using the exposure apparatus.
2. Description of the Related Art
Modified illumination techniques are employed to miniaturize the patterns of semiconductor devices. These techniques use an optimum effective light source distribution in accordance with a pattern to be formed. The effective light source distribution means the light intensity distribution on the pupil plane of a projection optical system when an object such as an original is not located on the object plane, and can also be interpreted as the angle distribution of a light beam which strikes a substrate. The effective light source distribution can be controlled by adjusting the light intensity distribution on the pupil plane (e.g., in the vicinity of the exit plane of a fly-eye lens) corresponding to the Fourier transform plane of the plane (object plane) on which an original (also called a reticle or a mask) is located in an illumination optical system. Examples of the modified illuminations are annular illumination, quadrupole illumination, and dipole illumination (Japanese Patent Laid-Open Nos. 11-87232 and 2003-318086).
Attention is focused on the influence that the symmetry of the effective light source distribution exerts on an image formed on the image plane of a projection optical system. Conceivable examples of factors that deteriorate the symmetry of the effective light source distribution are a manufacturing error of an optical element, and a change in light intensity distribution upon reflecting polarized light by a mirror. To improve the symmetry of the effective light source distribution, one proposed method is to adjust the positions of a plurality of independently drivable light-shielding plates in a plane perpendicular to the optical axis of the projection optical system while measuring the effective light source distribution (Japanese Patent Laid-Open Nos. 2004-247527 and 2006-19702).
Along with the recent advances in micropatterning of semiconductor devices, a demand for the symmetry of the effective light source distribution has become stricter. Under the circumstance, in a process of adjusting the symmetry of the effective light source distribution by driving the light-shielding plate, a targeted symmetry can rarely be obtained upon only one light-shielding plate driving. Gradually bringing the light-shielding plate to an optimum position by repeating light-shielding plate driving and effective light source distribution measurement many times is generally performed.
FIG. 7 is a flowchart showing a sequence of adjusting the symmetry of the effective light source distribution in a conventional method. In step S1101, the target position of the light-shielding plate is calculated. In step S1102, the light-shielding plate is driven to the calculated target position. In step S1103, the effective light source distribution is measured. In step S1104, the symmetry of the effective light source distribution is checked based on the measurement result of the effective light source. If the symmetry satisfies a standard value, the symmetry adjustment by driving the light-shielding plate ends. On the other hand, if the symmetry does not satisfy the standard value, the process returns to step S1101.
As described above, in the conventional sequence of adjusting the symmetry of the effective light source distribution by the light-shielding plate, effective light source distribution measurement and light-shielding plate driving based on the measurement result are performed many times, thus taking a long time. Note that one effective light source distribution measurement includes a process of sensing, by an image sensor built in a measuring device mounted on a substrate stage, an image formed on the image sensing plane of the image sensor, and converting the sensed image into an image on the pupil plane of the projection optical system.
The foregoing discussion is concerned with an improvement in symmetry of the effective light source distribution. However, the measurement time also is to be shortened when the effective light source distribution is controlled to a target effective light source distribution.